An integral part of microelectronic fabrication is the use of photoresists to transfer an image from a mask or reticle to the desired substrate circuit layer. After the desired image transfer has been achieved, the photoresist is removed, that is, stripped from the substrate before proceeding to some subsequent process step. Starting around 1980, amides and mixtures of amides with various co-solvents have routinely been used for this stripping step, see for example Ward et al., U.S. Pat. Nos. 4,395,479; 4,428,871 and 4,401,748.
Depending on the type of processing that is performed while the photoresist is in place on the substrate, the photoresist polymer may be cross-linked or hardened to the extent that amide-based solvents will no longer effectively strip the photoresist. Starting around 1985, the use of amide mixtures containing additional alkaline components, such as organic amines, (see Johnson U.S. Pat. No. 4,592,787; Merrem U.S. Pat. No. 4,765,844; Sizensky U.S. Pat. No. 4,617,251; Turner WO 87/05314 and Thomas et al. U.S. Pat. No. 4,791,043) or quaternary ammonium hydroxides (see Steppan et al. U.S. Pat. No. 4,776,892; Haq U.S. Pat. No. 4,744,834; Martin WO 88/05813) was introduced to facilitate the removal of such hardened photoresists.
The use of these alkaline components in strippers on microcircuits containing metals, particularly tungsten or copper and its alloys with aluminum, can lead to metal loss. Various types of metal corrosion, such as for example corrosion whiskers, pitting and notching of metal lines, have been observed during the use of these alkaline strippers. In the case of tungsten and copper corrosion can occur in the heated dry organic stripping composition mixtures with dissolved oxygen providing the cathodic reaction.
It would therefore be most desirable to be able to provide alkaline-containing photoresist stripping compositions suitable for stripping cross-linked or hardened photoresist polymer from substrates containing metal in which metal corrosion and/or metal loss is reduced or inhibited. A further object of this invention is to provide a method of stripping cross-linked or hardened photoresist from a metal-containing substrate using an alkaline-containing photoresist stripping composition containing an agent to reduce or inhibit such metal corrosion or metal loss.